1. Field of the Invention
This invention concerns the field of thickeners for cosmetic cleansing agents.
2. Description of the Related Art
Because cosmetic cleansing agents are often applied to vertical or otherwise non-level surfaces, it is considered advantageous for the formulation to have an increased viscosity so as to inhibit the propensity of the composition to flow. There are a variety of methods known to thicken compositions containing anionic surfactants. See Surfactants In Cosmetics, Vol. 16 of Surfactant Science Series, M. M. Rieger, Ed., Marcel Dekker 1985, Chap. 9, pp. 251-292, for a discussion of related topics.
U.S. Pat. No. 3,954,660 to Kennedy, et al. proposes increasing the viscosity of anionic surfactant slurries by admixing with such slurries an effective amount of an additive selected from the group consisting of dialkyl ethers, alkoxyethoxyethanols and tertiary amines having the general formula R.sub.3 N, wherein R is an alkyl group containing from 2 to 4 carbon atoms.
Polymeric thickeners are known to capitalize on the hydration and swelling properties of high molecular weight polymers and the chain extension and hydrogen-bonding of polymer units to achieve an increase in viscosity. European Pat. Nos. 132,961 and 133,345 disclose liquid soap compositions containing a water-soluble polymer selected from the group consisting of hydroxyethyl cellulose and hydroxypropyl guar. A quaternary nitrogen-containing cellulose ether thickening agent is disclosed as useful in the production of mild thickened liquid shampoo compositions in U.S. Pat. No. 3,962,418 to Birkofer.
Electrolytes such as sodium and ammonium chloride, by increasing the size of the surfactant micelles, are known to raise the viscosity of surfactant formulations. Long-chain lipophiles having a hydrophilic end-group such as alkanolamides, betaines and amine oxides are also known to increase viscosity by enlarging micelles. U.S. Pat. No. 4,375,421 to Rubin, et al. discloses solutions containing alkylamido betaines and certain water-soluble inorganic and organic salts. These salts have a viscosity-building effect on aqueous compositions containing alkylamido betaines in the presence of anionic surfactants. U.S. Pat. No. 4,490,355 to Desai teaches that a mixture of cocoamidopropyl betaine and oleamidopropyl betaine improves the thickening and foam boosting properties in hair and skin care formulations.
The viscosity enhancing effect of different amides on a 15% active monoethanolamine-lauryl sufate and a 15% active sodium laureth-2 sulfate has been reported. B. R. Donaldson and E. T. Messenger, Int. J. Cosm. Sci. 1:71-90 (1979). In a different report, cocamide MEA was found to be an effective thickener. G. Felletschin, Tensile Detergents 7:16-18 (1970). Further, U.K. Patent Application No. GB 2 143 841A discloses the use of a variety of thickeners, including long-chain (C.sub.12 -C.sub.18) fatty acid amides, as useful in thickened aqueous surfactant compositions.
It has also been proposed to thicken shampoos by combining two surfactants, one being a nonionic surfactant typified by dibasic and tribasic acid reaction products of alkoxylated polyol fatty esters and another being of a different type such as an amphoteric/anionic surfactant. U.S. Pat. No. 4,261,851 to Duke reports that the nonionic surfactant has a thickening effect on the composition.
Applicant has discovered that alpha-acetamido-fatty acid soaps having the general formula: ##STR1## wherein R is a hydrocarbon group containing from 10-20 carbon atoms and M is a cation, display much greater thickening power than the thickeners of the prior art. These thickeners have been found to raise the viscosity of anionic surfactant formulations by increasing the size of the surfactants micelles. U.S. Pat. No. 4,404,109 to Tellier, et al. discloses a surfactant having the formula: ##STR2## wherein R and R' are hydrocarbon groups and M is an alkali metal cation, as useful for the production of micro-emulsions in the presence of aqueous saline solutions in the assisted recovery of crude oil. Tellier, et al. describes a process that prepares a micro-emulsion of hydrocarbon and water containing a surfactant having the formula described above and a "cosurfactant," defined in the specification, examples and claims as a primary alcohol. Although it is stated that other surface-active co-agents may be used, no definition other than "the various alcohols" is provided.